The European Union warned Russia on Monday that there would be "consequences" for those involved in staging elections in Ukrainian regions seized by the Kremlin.
Moscow claimed Sunday that the United Russia party, which staunchly backs President Vladimir Putin, had won local ballots in areas occupied by Russia.
"We strongly reject this further futile attempt by Russia to legitimise or normalise its illegal military control and attempted annexation of parts of Ukrainian territories," the 27-nation bloc said.
"Russia's political leadership and those involved in organising them will face the consequences of these illegal actions."
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The EU has already imposed 11 rounds of unprecedented sanctions against Moscow since it launched its all-out invasion of Ukraine in February 2022.
The Kremlin claimed to have annexed four eastern and southern territories last year despite not having full military control over them.
Voting also took place in Crimea, annexed by Russia in 2014.
{{/usCountry}}Voting also took place in Crimea, annexed by Russia in 2014.
{{/usCountry}}The elections have been dismissed by Ukraine and its allies as a sham, and Kyiv's forces are fighting to claw back the territory seized.
The ballots were part of local polls held in Russia, which came ahead of presidential elections next year expected to prolong Putin's rule until at least 2030.
His opponents are in exile or jail and Moscow has criminalised criticism of its conflict in Ukraine and detained thousands for speaking out.